Primary human cytomegalovirus (HCMV) infection affects 1-3% of pregnancies, causing intrauterine growth restriction (IUGR) and permanent birth defects in 25% of congenitally infected babies. Symptomatic infants often succumb in the neonatal period, and most survivors have permanent debilitating sequelae, including mental retardation, vision loss and sensorineural deafness. This application builds on our knowledge of patterns of HCMV infection in the developing placenta and protection by maternal antibodies gained by studying the human placenta infected in vitro and congenitally infected in utero. How virus disseminates to the placenta and how immune defenses reduce HCMV replication are still unresolved due to the extreme host range restriction. A new severe-combined immunodeficient (SCID) murine model of human placental villi transplanted beneath the kidney capsule was established to study the vascular effects of fetal cytotrophoblasts in vivo. In human placental implants, cytotrophoblasts differentiate, undergo robust invasion of arterioles and migrate deep into the kidney parenchyma. The cells induce a dramatic lymphangiogenic response and formation of lymphatic vessels comparable to the human decidua. We have begun to study HCMV infection in human placental and decidual xenografts, also recently developed, and compare these with viral replication at the uterine-placental interface. Preliminary studies showed that the pathogenic strain VR1814 infected cytotrophoblasts and replicated in patterns that were comparable to those seen in congenitally infected placentas. In contrast to placental implants, virus spread extensively in infected decidual implants suggesting that different tissue environments affect levels of replication in vivo. Our overarching hypothesis is that (i) HCMV infection can be studied in a model of human placentation in SCID mice, (ii) pathogenic strains can be used to define determinants for viral tropism in cells within their tissue microenvironment, and (iii) neutralizing anti-HCMV antibodies reduce infection in the placenta. Further, we propose that IFN-? modulates viral replication in vivo. Confirmation of this hypothesis will be directly relevant to clinical applications for the prevention of congenital infection and disease. The specific aims are as follows. Aim 1. Study HCMV replication and virus dissemination in placental and decidual implants in a model of human placentation in SCID mice. Aim 2. Evaluate HCMV replication in human placental and decidual implants in the presence of virus neutralizing antibodies and IFN-? expression. Especially important for clinical applications will be firmly establishing the utility of human placental implants to evaluate HCMV pathogenesis and novel antiviral strategies tailored to reduce infection in the uterine and placental microenvironments. PUBLIC HEALTH RELEVANCE: Information from studies of HCMV infection in human placental and decidual implants in the severe combined immunodeficiency (SCID) mouse model will lead directly to practical application of new clinical interventions that reduce viral replication at the uterine-placental interface, assess viral proteins with potential use in diagnostic tests, identify viral glycoproteins that elicit potent neutralizing antibodies, and develop novel strategies to bolster innate immune defenses in the placenta.